Japanese Patent Application Laid-Open Publication No. 2002-104694 (Patent Document 1), for example, discloses a laser printer, which is an image forming apparatus of electronic photography type. The laser printer includes a fixing unit. The fixing unit has a heating roller and a pressing roller. The heating roller incorporates a halogen lamp that generates heat. The pressing roller presses the heating roller. More precisely, the pressing roller can press a paper sheet onto the heating roller when the paper sheet, which has a transferred toner image, passes through the nip between the heating roller and the pressing roller. When the pressing roller presses the paper sheet to the heating roller, the toner image is fixed on the sheet because of the heat applied to the sheet from the heating roller.
The paper sheet having the toner image thus fixed is conveyed forward and finally discharged onto a discharged-sheet tray trough a sheet discharge path. If a plurality of paper sheets are discharged, they are laid, one on another, on the discharged-sheet tray in the order they have been discharged.
In the laser printer described in Patent Document 1, a toner image is thermally fixed on the paper sheet. Therefore, the sheet may curl after the thermal fixing of the image.